Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al2O3-4 Wt Pct Nb2O5 Ceramic Compound

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 48; no. 10; pp. 4432 - 4440
• Main Authors: Santos, J. L., Marçal, R. L. S. B., Jesus, P. R. R., Gomes, A. V., Lima, E. P., Monteiro, S. N., de Campos, J. B., Louro, L. H. L.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.10.2017; Springer Nature B.V
• Subjects: Alloys; Aluminum oxide; Binder removal; Ceramics; Characterization and Evaluation of Materials; Characterization of Minerals; Chemical bonds; Chemical composition; Chemistry and Materials Science; Densification; Fluorine; Materials 2017; Materials Science; Metallic Materials; Metals; Nanotechnology; Niobium; Polyethylene glycol; Polyethylenes; Scanning electron microscopy; Sintering; Structural Materials; Surfaces and Interfaces; Theoretical density; Thermal analysis; Thin Films; Topical Collection: Characterization of Minerals; X-ray diffraction
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-017-4271-y

Different amounts of LiF were added to an Al 2 O 3 -4 pct Nb 2 O 5 basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb 3 O 7 F, but also to the absence of LiAl 5 O 8 . The preferential interaction of LiF with Nb 2 O 5 , instead of Al 2 O 3 , contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.